(1) Field of the Invention
The present invention relates to novel polycarbonates, to processes for the preparation of these polycarbonates, and to novel dihydric phenols that are the raw material for the preparation of the polycarbonates. Particularly, the present invention relates to novel polycarbonates that exhibit excellent optical properties such as high refractive index and are useful as, for example, materials for optical devices.
(2) Description of the Prior Art
As typical polycarbonate resins, resins obtained by reacting 2,2-bis-(4-hydroxyphenyl)propane (Bisphenol A) with phosgene or diphenyl carbonate are known. These resins are widely used as engineering plastics in many fields since they have excellent properties; i.e., high transparency, high thermal resistance, excellent mechanical properties, high dimensional accuracy in molding, etc.
In recent years, the demand for plastic optical elements has been risen since they are more advantageous over glass ones in such aspects that they are lighter in weight; they are excellent in impact strength; polishing is unessential; mass production are easier; and the mass production of nonspherical lenses is possible. While it is known that polycarbonates due to their excellent transparency and optical properties such as high refraction index are useful as materials of the plastic optical elements (c.f. Japanese Patent Application Kokai No. 126119/1983 and Japanese Patent Application Kokai No. 179224/1983), the development of novel materials having excellent optical properties has been required with the increase of the application fields of optical elements.